Thomas was born in 1574,[1] probably at Lixnaw, the eldest son of Patrick Fitzmaurice, 17th Baron Kerry and his wife Joan (Jane) Roche.
After the death of his father in August 1600 and the capture of Listowel Castle by Sir Charles Wilmot in November, he found himself excluded by name from all pardons offered to the rebels.
On 26 October 1603 Sir Richard Boyle noted that he was still operating actively in Munster, but with a small force, and was trying to find pardon from the new king, James I.
He sat in the Irish parliament of 1615, when a quarrel arose between him and Lords Slane and Courcy over a question of precedency, which was ultimately decided in his favour.
After a short period of restraint he appears to have agreed to fulfil his contract, and was allowed to return home.